Image sensing devices made up of an array of laterally spaced sensors are well known and can take a variety of forms. The array can be viewed as being made up of a number of laterally offset regions, commonly referred to as pixels, each containing a separate sensor. The art has recognized that sensing advantages can be realized by forming a convex lens surface for each pixel, the overall resulting surface being referred to as a lenticular surface. The following teaching is considered to be representative:
R-1 Whitmore U.S. Pat. No. 4,362,806, note particularly FIG. 10, and column 44, lines 41 through 63.
A variety of multipixel semiconductor devices are known. There have been teachings of improving their light sensing properties by forming semicylindrical lenses in a surface resin layer. The semicylindrical lenses are formed by patterning a phenol-novolak system (i.e., a positive-working photoregist) and then heating the resin remaining to a temperature above its glass transition temperature. Individual resin domains flow laterally, causing a convex surface to the be formed. These teachings are illustrated by the following:
R-2 Ishihara et al, "A High Photosensitivity IL-CCD Image Sensor with Monolithic Resin Lens Array", LEDM, 19.3, pp. 497-500 (1983);
R-3 Miyata Japanese Kokai 59-147,586, published Aug. 23, 1984;
R-4 Miyata Japanese Kokai No. 59-148,482, published Aug. 25, 1984;
R-5 Saeki et al, "Effect of Microlens Array on MOS Color Imager", IEEE Transactions on Consumer Electronics, Vol. CE-31, No. 2, May 1985.
In considering the prior state of the art it is, of course, important to differentiate between schematic diagrams of constructions hypothesized and the structures which were actually realized in practice. In the reported devices actually constructed a number of difficulties have been encountered. The lens curvature has been less than that desired, and the optical clarity of the lens forming material has been limited. In fabrication lateral spreading of domains of lens forming material has been observed to occur when the lens forming material of the domains is put in a fluid form as required to achieve the convex lens surface. This has complicated area definition and resulted in rapid loss of surface curvature when material from adjacent domains has come into contact. While low lens curvature can to some extent be compensated by increasing the thickness of the layers separating the lens from the underlying sensing element of the semiconductive substrates, difficulties have been encountered in constructing these separating layers. Although time consuming multiple laydowns of materials forming the separating layers have been practiced, overall layer thicknesses have remained below optimum levels for optical purposes. Finally, the lens shapes attempted have been of less than optimum optical configuration. Thus, while the advantages of lenticular surfaces for multipixel semiconductor sensor arrays have been postulated, their advantages have remained largely unrealized.